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1. Field of the Invention
The present invention relates in general to a sensing device and method, and more particularly to a sensor and method for increasing signal response time. The present invention also relates to a limit sensor or a switch for sensing travel of a moveable element on a selected path of movement.
2. Description of the Related Art
Compression or force sensitive resistors are commercially available for a variety of applications. A force sensitive resistor normally resists the flow of electrical current, but permits the flow of electrical current in proportion to pressure applied to the resistor. As the resistor is compressed, it becomes less resistant to the flow of current so that the current flow may be measured by a suitable detector which indicates the application and the amount of pressure thereon. A force sensitive resistor may be made of an elongated printed circuit strip having electrically conductive strips printed upon a nonconductive substrate. The conductive strips terminate in two electrical terminals or leads. An electrically resistive film or layer is applied thereon such that the resistive film lies across and against the conductive strips. As a force is applied against the resistive film, the electrical resistance decreases between the terminals. Polymer thick film (PTF) resistors are commercially available from a variety of suppliers including Eaton Corporation for example.
U.S. Pat. No. 4,799,381 describes the use of a force sensing resistor embedded in a resilient, rubber like strip as a vehicle road and/or weight sensor.
Other vehicle applications for such sensors include applying a force sensitive resistor in a vehicular braking system for creating output signals to a logic circuit as disclosed in U.S. Pat. No. 5,010,972.
U.S. Pat. No. 5,435,409 discloses the use of a force sensing resistor functioning as a deformation sensor as a safety device for the protection of vehicle occupants against a side-on collision.
Still another application for a force sensing resistor is as an electronic push button assembly useful in elevator controls as described in U.S. Pat. No. 5,477,942.
In some applications, for example, when a door jamb switch is employed in a power sliding door system for a vehicle, the vehicle controller or processor requires that a signal be sent to engage the hold open latch on the door. The door strikes the door bumper as it reaches its end of travel when it opens and applies a force, and then typically rebounds. The time that the door was in contact with the bumper is often too short for the processor to receive and recognize the signal. After rebound, the end of travel switch could be in an inactive state. When the operator wishes to close the sliding door, one of the command switches is depressed or activated. If the processor does not know the state of the door, it defaults to opening the door. So, the processor sends a command signal to the door module to open the sliding door which, will activate the end of travel switch which will engage the hold open latch. This will cause operator aggravation because the door will not close without the hold open latch being engaged.
While the signal time could be electrically lengthened using conventional electronic circuitry, there still exists a need for a sensor that increases the length of time of the impact force on the sensor, and transfers that force signal to the appropriate processor. Such a sensor should preferably stay activated during the complete cycle of movement including during any over travel or rebound effects. The sensor preferably should remain inactive (or open) when the door is closed. The sensor should signal the open/closed status of a power sliding door accurately to the vehicle processor. When the door is fully opened, the sensor would tell the processor that the door is open. To close the door would simply require input from the vehicle operator or occupant by way of a door activation switch on the instrument panel or other portion of the vehicle. Preferably, such a sensor will be a force sensitive resistor such as a proportional input device (PID) enclosed by a switch housing and actuator assembly. Also, the sensor would advantageously utilize the time delay effect due to rubber dampening.
While the sensor would be particularly suited for vehicle applications, such as end of travel of a moveable element and the status of that moveable element, it would also be useful in other applications. As an end-of-travel switch, it would assure latch engagement.
The present invention is directed to solving the aforementioned problems as well as others by providing an improved sensor for increasing signal time by utilizing a dampening effect of an elastic material having a selected resiliency for providing a time delay in the signal. The present invention comprises an actuator having a resiliently deflectable member that receives a force from a moveable element and transfers the force to a pressure sensitive signal element. A base member supports the pressure sensitive signal element and the actuator. The selected resiliency of the resiliently deflectable member increases the signal time by using the dampening effect of the resilient material. In a preferred embodiment, this is used for xe2x80x9cpulse stretchingxe2x80x9d a pulsed voltage signal.
The present invention is also directed to a limit sensor that comprises a pressure sensitive signal element operatively connected to a moveable element for receiving a force from the moveable element as it travels on its path of movement. The pressure sensitive signal element establishes a signal indicative of the force. A resiliently deflectable member activates the signal at a predetermined location along the path and applies a controlled force against the pressure sensitive signal element that is proportional to the input of the transferred force. A base member supports the resiliently deflectable member and the pressure sensitive signal element in the limit sensor according to the present invention.
An object of the present invention is to provide a sensor for increasing signal time with a selected resiliency of a resiliently deflectable member.
Another object of the present invention is to provide a sensor for increasing signal time with the use of an elastic material.
Another object of the present invention is to provide a sensor for increasing signal time with the use of a rubber material.
Another object of the present invention is to provide a method for increasing signal time by using a material having a selected resiliency to create a dampening for a time delay.
Another object of the present invention is to provide a limit sensor that functions as an end of travel switch.
Still another object of the present invention is to provide a limit sensor that functions as an end of travel switch for a power sliding door for a vehicle.
Still another object of the present invention is to provide a method of sensing the position of a moveable element.
Still another object of the present invention is to provide a method for sensing the state of a sliding door as it nears its end of travel.
Still another object of the present invention is to provide an improved sensor that is simple in design, rugged in construction, and economical to manufacture.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is described and illustrated.